Optical fiber connectors are an essential part of substantially all optical fiber communication systems. For instance, such connectors are used to join segments of fiber into longer lengths, to connect fiber to active devices such as radiation sources, detectors and repeaters, and to connect fiber to passive devices such as switches and attenuators. The principal function of optical fiber connectors is to hold an optical fiber such that its core is axially aligned with the optical path of the device to which the connector is mating (e.g., another fiber). This way, the light from one fiber is optically coupled to the optical path of the mating device.
It is common in applications using single mode fibers to use connectors that ensure physical contact between the fibers in order to reduce power losses, such as Fresnel losses. These connectors are known as physical contact (PC) connectors or angled physical contact (APC) connectors. PC connectors create a physical contact between two fibers that have been polished flat on the fiber ends. APC connectors ensure physical contact between two fibers that have polished beveled end faces. The beveled end face is usually about 8° off perpendicular from the optical transmission path of the fiber, and insures that any light which is reflected from the end face interface is not reflected back down the optical transmission path. This way, damage to the light generating source (e.g. laser) is avoided. Since the end faces of mating optical fibers in an APC connector are beveled, if they are not rotationally aligned with one another, their bevels will not be complementing. Instead, they would be interfering such that a gap between the end faces results when the fibers are mated. Therefore, to ensure that the beveled end faces mate in a complementary fashion, it is essential that each fiber be held in the mating connectors in a particular rotational position.
Other fiber types also require precise rotational alignment of the fiber. Polarization maintaining (PM) fibers (i.e., PANDA fibers or bifringent fibers) have a particular orientation to the path that the light within the fiber travels. Connectors for these fibers need to ensure that the rotational alignment of the fibers is kept constant across the fiber connection in order to preserve the state of linear polarization from a coherent laser source (e.g., a distributed feedback laser). The orientation is determined by measuring the relative power between the two orthogonal fiber axes (i.e., the extinction ratio) prior to assembling the connector. During assembly, the fibers are kept in the predetermined position to avoid radial misalignment.
Conventional methods of rotationally aligning fibers require the fibers to be polished and the proper alignment position to be measured prior to the assembly of the connector. As a result, however, such connectors are subject to optical power loss caused by eccentricities within the connector. Often times, when a fiber is affixed to a ferrule, its center location is eccentric relative to the outer diameter of the ferrule. The cause of the eccentricity can be because the fiber core is not perfectly concentric within the optical fiber, or because the bore hole in the center of the ferrule might not be perfectly concentric relative to the ferrule outside diameter, or because the fiber might not reside perfectly concentric in the bore hole. All of these conditions can result in the cores of the two mating fibers in a connector unit failing to be perfectly aligned. Eccentric misalignment of the fiber cores creates optical power loss across the fiber connection.
Correcting for core eccentricities would require the mating ferrules of a connector to be positionally adjusted relative to one another. However, in existing connectors such adjustment is not possible because it would result in a loss of the rotational alignment of the fibers with respect to each other. For example, an APC connector could not be adjusted at this point because the beveled faces of the fibers would lose their complementing position. A connector using PM fibers could not be adjusted at this point because the polarizing rotational alignment of the fibers has been predetermined and would be lost by any further adjustment. Because any rotational alignment of the fibers is performed prior to connector assembly, conventional connectors do not allow for ferrule adjustment to reduce such losses caused by eccentricities.
There is a need for a connector that allows the eccentricities of the fiber cores to be minimized, while maintaining the fiber rotational alignment when necessary such as in PM applications and APC applications. The present invention fulfills this need among others.